With green awareness on the rise, there is an increasing demand for a lead-free process applicable to printed circuit board assembly (PCBA) technology. For example, nowadays, printed circuit board assembly no longer employs a tin-lead solder but employs a widely-used tin-silver-copper (SAC) alloy solder or tin-copper alloy solder. Normally, the melting point of lead-free solders, tin soldering temperature, and wave soldering temperature are 20° C. to 30° C. higher than that of tin-lead solders, not to mention that lead-free solders adhere to tin less readily; as a result, assembly process providers usually raise the temperature of tin in operation with a view to enhancing the processability thereof.
During a typical printed circuit board assembly process, some thermal sensitive components can only withstand the thermal stress of a eutectic solder at low temperature, but the thermal sensitive components do not meet the high temperature requirements of a lead-free process. For example, constituent components of a liquid crystal display (LCD) include a printed circuit board, and the liquid crystal display cannot withstand the thermal stress of a lead-free wave soldering process.
To overcome the aforesaid limitation of thermal sensitive components, it is often feasible to assemble a liquid crystal display by means of hand soldering. However, the aforesaid conventional process is unreliable, cost-ineffective, and inefficient, when compared with an automated process.